GRB 200711A: Swift-XRT refined Analysis

We have analysed 6.9 ks of XRT data for GRB 200711A (Marshall et al. GCN Circ. 28078), from 150 s to 40.4 ks after the BAT trigger. The data comprise 29 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 1145 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 285.97020, -0.14708 which is equivalent to: RA (J2000): 19h 03m 52.85s Dec(J2000): -00d 08' 49.5" with an uncertainty of 1.6 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=0.51 (+0.13, -0.14), followed by a break at T+3349 s to an alpha of 1.41 (+/-0.09). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.01 (+0.22, -0.21). The best-fitting absorption column is 1.65 (+0.30, -0.27) x 10^22 cm^-2, in excess of the Galactic value of 5.7 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.6 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.65 (+0.30, -0.27) x 10^22 cm^-2 Galactic foreground: 5.7 x 10^21 cm^-2 Excess significance: 6.5 sigma Photon index: 2.01 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 1.41, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.4 x 10^-13 (1.1 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00981957. This circular is an official product of the Swift-XRT team.